The overall objective of this application is to establish new mouse models of fibrotic diseases. To achieve this objective we propose two approaches, one is to disrupt in fibroblasts of transgene mice the TGF- beta signalling pathway, the other is to alter the balance between metalloproteinases and their tissue inhibitors in the extracellular matrix of fibroblasts. Our application is anchored on our previous identification and characterization of a promoter/enhancer in the mouse gene for the proalpha2 chain of mous4e type I collagen (Co11alpha2) that has the ability to direct expression of reporter genes specifically to fibroblasts of transgene mice. To avoid undesirable effects during embryonic development we use a dual system. This system, based on Cre mediated recombination, allows to switch-on the DNAs that we propose to activate in fibroblasts at a specific time after birth. The system used throughout this proposal is based on a Cre recombinase, developed by others, which becomes activated only after administration of Tamoxifen. In this proposal, expression of the DNA for this recombinase is directed by the Co11alpha2 promoter/enhancer which restricts its expression to fibroblastic cells. The genes that we propose to express in fibroblasts postnatally are cloned downstream of the potent and ubiquitously active ROSA26 promoter. Interposed between this promoter and the DNAs that we propose to express we placed a transcription stop cassette, flanked by two Lox P sites, which are substrates for Cre recombinase. Thus expression of the DNAs is only possible after Cre-mediated removal of the STOP cassette. Hence in this dual system, Tamoxifen controls expression of these DNAs which is restricted to fibroblasts because Cre is only expressed in fibroblasts. We hypothesize that the expression of DNA for a constitutively active TGF-beta1 receptor in fibroblasts as well as the over-expression of TIMP1, in fibroblasts will produce fibrotic phenotypes. To attempt to correct the postulated fibrotic phenotype caused by expression of the constitutively active TGF-beta type I receptor, we propose to over- expression in fibroblasts a DNA for a dominant-negative Smad3. In each case of the phenotype of transgene mice and that of their fibroblasts in culture will be extensively characterized with the use of specific molecular markers and gene expression arrays. The results of such gene profiling of fibroblasts from fibrotic animals will also be compared to those performed with fibroblasts of scleroderma patients performed by Dr. Frank Arnett.